Spectroscopic light source and method



Sept. 25, 1962 A. C. DUCATI ET AL SPECTROSCOPIC LIGHT SOURCE AND METHOD Filed Feb. 24, 1959 0019/47/10 C 1/6 7 VEQA/Q/V/Z BLOCK/MON INVENTORS States Patent @tlhce 3,055,262 Patented Sept. 25, 1962 SPECTROSPI LIGHT SOURCE AND METHOD Adriano C. Ducati, Corona Del Mar, and Vernon H.

Blacinnan, Laguna Beach, Calif, assignors to Plasmadyne Corporation, Santa Ana, Calif., a corporation of California Filed Feb. 24, 1959, Ser. No. 795,062 4 Claims. (Cl. 83-14) This invention relates to a photographic light source and method. More particularly, the invention relates to a spectroscopic lamp and to a method of forming spectra.

There is a number of situations, particularly in spectroscopy, where it is desirable to provide a light source which is illuminated for only a very short period of time, on the order of microseconds or less. In addition, it may be highly important that the light source be capable of heating a substance, which is to be the subject of spectrum analysis, to a sufiiciently high temperature that the resulting spectrophotograph will illustrate the substance in a highly excited state. Such heating must be accomplished without contamination of the substance, such as by electrode material or by the envelope in which the substance is contained. In producing spectrophotographs, schlieren photographs, and the like, it may be highly desirable to flash the light source many times during a single second in order that pressure differences, changes in energy level, etc., may be detected.

In view of the above factors relative to such arts as spectroscopy, schlieren photography, and the like, it is an object of the present invention to provide a photographic light source which is illuminated for only a very small fraction of a second and which may be repetitively operated a large number of times per second.

A further object of the invention is to provide a spectroscopic lamp which effects substantially instantaneous heating of a test substance to a very high temperature.

A further object is to provide a method of forming spectrophotographs, schlieren photographs, etc., in a highly simple yet accurate and effective manner.

A further object is to provide a method of forming a spectrophotograph, or a series of spectrophotographs taken in rapid sequence, without effecting contamination of the test substance by electrode, envelope or other material.

These and other objects and advantages of the invention will be set forth more fully in the following specification and claims, considered in connection with the attached drawing to which they relate.

In the drawing:

FIGURE 1 is a schematic elevational view illustrating a photographic light source constructed in accordance with the present invention, in combination with means for charging such source with gas and for energizing such source to effect illumination thereof;

FIGURE 2 is a schematic view illustrating the combination of the light source with a lens system and spectroscope; and

FIGURE 3 is a transverse section taken on line 33 of FIGURE 1.

Referring to the drawing, and particularly to FIGURE 1, the photographic light source, or spectroscopic lamp, is indicated generally at as comprising an elongated tubular envelope 11 having opposed ends 12 and 13 which are illustrated as being rounded. Envelope 11 is formed of a suitable heat-resistant non-conductive transparent substance such as quartz or the like, and may have a small diameter on the order of inch. Mounted concentrically around the central portion of envelope 11 is a tubular conductor 14 which is provided with a longitudinal slit or gap 16. Conductor 14, which may be formed of copper or other highly-conductive material, therefore comprises a single-turn circuit. It is preferred that the conductor 14 fit closely around envelope 11 as best shown in FIGURE 3.

Means are provided to supply a very short, high-current pulse (or pulses) of current to the conductor 14 on opposite sides of slit 16-, so that the current flows circumferentially around the envelope 11 through the abovementioned single-turn circuit. Such means are illustrated to comprise conductors or legs 17 and 18 formed integral with conductor 14 at one end thereof and on opposite sides of the slit 16. Conductors 17 and 18 are connected, respectively, to relatively short leads 19 and 26 leading to a low-inductance capacitor means 21. A suitable triggering means 22, for example of the spark-gap type embodying a suitable triggering or ionizing electrode, is interposed in the lead 20 in order to effect discharge of capacitor 21 through the leads 19 and 20, legs 17 and 18 and the single-turn conductor 14. The capacitor 21 is associated with conductor 14 in low-inductance arrangement, so that the capacitor will discharge in a very short period of time which may be less than a microsecond. Suitable means, indicated at 23, are connected through leads 24 and 25 to the capacitor 21 in order to effect charging thereof, it being understood that the charging means may be disconnected from capacitor 21 prior to operation of trigger 22.

It is within the scope of the invention to provide means for supplying high-current pulses in rapid sequence to conductor 14. Such means may comprise a bank of capacitors which appropriate sequentially-operated trigger means, and may also comprise a suitable resonant network associated with the capacitor means.

Means are provided to charge envelope 11 with the substance which is to be the subject of a spectrophotograph, schlieren photograph, etc. These means are illustrated to comprise a suitable source of gas 26 which is connected through a conduit 27 to the end 12 of envelope 11. A second conduit 28 is connected to the other end 13 of the envelope and has a pump 29 interposed therein in order to draw gas through the envelope for discharge to the atmosphere or to a suitable container. A valve 31 is mounted in the first-mentioned conduit 27 to start and stop the gas flow.

Referring to FIGURE 2, the apparatus further comprises a suitable camera 32 of the type conventionally employed in forming spectrophotographs or schlieren photographs, etc. Camera 32 is associated with a lens means 33 which extends therefrom to the slit 16 in conductor 14.

In performing the method of the invention, for example with the apparatus described and illustrated herein, pump 29 is first operated, with valve 31 open, to effect flow of the test gas from source 26 through conduits 27 and 28, as well as through envelope 11. This is continued fora period of time sufficient to be sure that the only substance in the envelope 11 is the gas from the source 26. In the present description, it will be assumed that it is desired to make a spectrophotograph of the gas, although the applicability of the method to schlieren photography and certain other processes will be appreciated by those skilled in the art.

Capacitor 21 is then suitably charged by means of charging circuit 23, after which trigger 22 is operated to discharge the capacitor through leads 1720 and through the single-turn conductor 14 circumferentially around the axis of envelope 11. The circuit parameters are so se lected that capacitor 21 Will discharge in a very short period of time, for example a microsecond, and will deliver a very high current such as ten thousand amperes.

The flow of current circumferentially around envelope 11 is concentrated at the interior surface of the conductor 14, due to skin effect, and results in the formation of an induced current sheet flowing in the gas within envelope 11. Such induced current sheet flows in the opposite direction from the direction of current flow through conductor 14, and is initially relatively close to the interior wall of the non-conductive envelope 11.

The sheet of induced current, composed of ions and electrons, acts as a barricade through which the lines of magnetic force, which are generated due to the circumferential current flow through conductor 14-, may not penetrate appreciably. This is particularly true when the rate of change of magnetic field strength is great. This being the case, at least a majority of the lines of magnetic force initially pass (in a tubular configuration, longitudinally of envelope 11) between the inner surface of conductor 14 and the current sheet flowing in the gas within envelope 11, that is to say through the quartz or other envelope material.

The generally tubular magnetic field collapses immediately and acts as a piston to drive (implode) the current sheet (ions and electrons) radially inwardly toward the axis or center of envelope 11. As the current sheet collapses toward the center, in a shock wave, the gas is compressed and greatly elevated in temperature because of the speed and collision of particles. The inward movement, or implosion, continues until the external magnetic pressure is counterbalanced by the internal pressure resulting from the compression and the temperature increase.

It is pointed out that the ends of the conductor 14 are open (not formed of electrically-conductive material). Thus, there are end openings through which the lines of magnetic force may pass to form continuous loops having portions located externally and internally of the conductor 14. No electrical conductors should be disposed close to the conductor 14 to interfere with the external portions of the closed loops.

The result of the above-described implosion is that the gas within envelope 11 becomes greatly heated and is brightly illuminated. The greatest heat, and the highest-intensity light, are generally along the axis of the envelope, parallel to gap 16. The lens system 33 therefore receives, through gap or slit 16, light rays which represent the gas in a very highly excited condition.

Under certain conditions, the high temperature within envelope 11 may cause contamination of the gas by means of material from the envelope. Such contamination may result from contact between the end walls and the very high-temperature gas at the envelope axis. However, any such contamination is rendered unimportant since the lens means 33 is directed at the gas in the center of the tube, radially adjacent slit 16. Even when the system is repetitively operated, as above-indicated, a large number of pulses will occur before the gas adjacent end 12 travels from such end to the region of slit 16.

The gas pressure within the envelope may vary through a wide range, depending upon the particular conditions desired. For example, the gas pressure may range from 0.10 atmosphere down to atmosphere or even lower.

To aid in the above-described implosion action, the gas flowing through the envelope 11 may be pro-ionized such as by passing radio-frequency waves through the cavity within the envelope. For example, electrodes (not shown) may be located near the opposite ends 12 and 13 of the envelope and energized by a radio-frequency oscillator. Such pre-ionization increases the electrical conductivity of the gas, and thus the amount of current flow in the above-indicated current sheet.

It is to be understood that the envelope 11 may comprise a sealed tube which may, for example, serve as a standard. Thus, a large number of sealed tubes 11 may be provided, each containing a different gas, to form a set of standards.

Various embodiments of the present invention, in addition to what has been illustrated and described in detail, may be employed without departing from the scope of the accompanying claims.

We claim:

1. A method of spectroscopy, which comprises providing an elongated envelope formed of light-transmissive insulating material, introducing a test gas into said envelope, disposing concentrically around the mid-portion of said envelope a single-turn electrical conductor having a slit or gap therein longitudinally of said envelope, discharging a capacitor through said single-turn circuit to form a current pulse having an order of magnitude at least in the range of thousands of amperes and continuing for a time period on the order of microseconds to thereby effect a magnetic implosion in said envelope and consequent extreme excitation, heating and luminosity of said gas in said envelope, and bringing a spectroscope to bear on said gas at said slit or gap to form a spectrum representing said gas.

2. A spectroscopic light, comprising an elongated smalldiameter envelope formed of light-transmissive non-conductive material and containing a test gas, a generally tubular electrical conductor mounted closely around said envelope at the central portion thereof and generally concentrically therewith, said conductor having a slit formed longitudinally therein and causing said conductor to comprise a single-turn electrical circuit, said slit being adapted to transmit light, capacitor means, and means to discharge said capacitor means through said singleturn circuit in such manner that a magnetic implosion is created in said envelope causing extreme heating, excitation and luminosity of said test gas.

3. The invention as claimed in claim 2, in which gas supply and discharge means are associated with said envelope and include means to cause flow of gas into one end of said envelope and means to pump gas out the other end thereof whereby said gas flows longitudinally through said envelope.

4. The invention as claimed in claim 2, in which said capacitor means is adapted to feed a current pulse of at least thousands of amperes through said conductor for a time period on the order of microseconds.

References Cited in the file of this patent UNITED STATES PATENTS 1,698,691 Buttolph Jan. 8, 1929 1,871,226 Skala Aug. 9, 1932 2,149,414 Bethenod Mar. 7, 1939 2,544,078 Glassbrook Mar. 6, 1951 2,753,479 Aughey et al July 3, 1956 2,800,622 Lion July 23, 1957 2,817,032 Batteau Dec. 17, 1957 2,883,580 Kilpatrick Apr. 21, 1959 2,939,048 Waniek May 31, 1960 

